Pumps, such as those used in the chemical, petrochemical, or pharmaceutical industries, employ diaphragms to separate the fluid being pumped from the fluid which initiates diaphragm actuation. Typically, these diaphragms are made of rubber, and undergo extensive repetitive flexing while in use. In many instances, the fluid being pumped is of a corrosive nature which often causes a diaphragm to fail rapidly. Failure of the diaphragm may result in corrosive liquid contaminating equipment. A diaphragm failure may also cause the release of chemicals to an air stream that subsequently gets released into the environment where it may result in further damage or injury.
To protect against such failure, many attempts have been made to extend the lives of such diaphragms. Often, chemically resistant materials such as polytetrafluoroethylene (PTFE) are used as an overlay to a rubber diaphragm so that the rubber is protected from the corrosive chemicals. This type of construction also has utility in protecting high purity fluids from contamination due to rubber degradation. In other instances, a chemically resistant material is used as the sole material of construction of the diaphragm. However, when PTFE is used as the sole material, or when used as an overlay, the PTFE fatigues more readily from flexing as compared to conventional rubbers.
Failure of a diaphragm is normally preceded by the development of minute cracks, tears, and other discontinuities that propagate until there is a complete failure, at which time there is an unwanted passage of liquid between pump chambers. Attempts have now been made to predict beforehand the oncoming failure of a diaphragm. Such attempts include use of an electrically conductive material extending within a nonconductive, chemically inert diaphragm, as described in U.S. Pat. No. 4,569,634. The electrically conductive material is in the form of a mesh screen, or web of conductive fibers and is designed to be spaced equally from both faces of the diaphragm. The use of such screens, meshes, or fibers within a nonconductive, chemically inert material, such as PTFE, causes abrasions within the nonconductive material, particularly when undergoing extensive flexing, which shortens the useful life of the diaphragm.
Copending U.S. Pat. application Ser. No. 08/110,684 provides for a prefailure warning pump diaphragm in which a barrier sheet of PTFE has embedded within it a thin flexible conductive fiber made of conductive PTFE. Before the onset of failure, the conductive fiber detects the change in conductivity by suitable electronic means which signals imminent failure. However, change in fiber resistivity is very difficult to detect. Also, only a finite area of the face of the diaphragm is covered by the fiber, thus creating a possibility for an undetected failure.
Other commercially available products include a Wil-Gard.TM. I Diaphragm Monitoring System made by Wilden Pump and Engineering Co., of Colton, Calif. This device provides for a resistivity sensor located between a PTFE overlay and a backup elastomeric material. This device also only detects leakage after the diaphragm has failed. Moreover, additional and substantial damage may occur if corrosive chemicals cause deleterious effects to the elastomeric backup material.
Finally, other types of leak detection devices for pumps have been developed. U.S. Pat. No. 5,062,770 to Story, et al. provides for a containment chamber in a pump after the PTFE diaphragm has failed. Unfortunately, such devices do not detect pre-failure conditions.
There is a need for a diaphragm that detects pre-failure conditions across the entire surface of the diaphragm, provides for a longer useful life of the diaphragm and is easily applied to conventional pumps without any design changes of the pump.